1. Field of the Invention
The present invention relates to a helically-scanned rotating-head type recording/reproducing apparatus for recording and reproducing code data, audio information, video information, and so forth onto and from a tape-shaped recording medium.
2. Description of the Prior Art
A rotating head type recording/reproducing apparatus that records and reproduces digital audio data or digital/analog video data onto and from a magnetic tape that is guided and travelled on a cylinder surface of a drum through rotating heads is known. When such data is recorded on the magnetic tape, slant tracks are successively formed thereon. When the recorded data is reproduced, the tracks should be precisely scanned by the heads. The technique for causing the heads to precisely trace the tracks is referred to as tracking control.
Various tracking control techniques have been proposed. In one technique, a control (CTL) signal is recorded in longitudinal direction of a magnetic tape at predetermined pitches so as to keep the phase of the reproduced CTL signal constant. In this method, magnetic heads dedicated for recording and reproducing the CTL signal are required. Similar problem will take place in a method that uses rotating heads for tracking control rather than fixed heads. In an 8-mm VCR, pilot signals with four frequencies are frequency multiplexed with recorded analog signal so that they are recorded on four successive tracks. The method that frequency multiplexes the pilot signals is not used for an apparatus that records and reproduces the base band of digital data because it is difficult to multiplex and separate frequencies of the pilot signals.
A method that is applicable for recording and reproducing digital data and that does not need to use heads dedicated for tracking control is employed for a digital audio tape recorder (DAT). In this method, an ATF (Automatic Track Finding) pilot signal is recorded in a predetermined region of a track. The tracking condition is determined corresponding to the relation of the signal levels of two pilot signals reproduced from two adjacent tracks (see U.S. Pat. No. 4,739,420). The DAT uses rotating heads with different azimuths (which represent angles against the extended directions of gaps of the heads) so as to decrease crosstalk that takes between adjacent tracks. Thus, to reproduce pilot signals from the adjacent tracks, low frequency (large wavelength) pilot signals, which have low azimuth loss, are used.
To reduce the size of the rotating heads or rotating transformers and simplify the construction thereof, an overwrite erasing system that does not use rotating erasing heads is preferably employed. However, since signals with long wavelength are recorded to a deeper portion of the magnetic tape, they are not easily erased by overwrite operation. In particular, these signals are not easily erased by signals with short wavelength such as digital data. Thus, to erase the pilot signal, a special erase signal with a wavelength longer than that of recorded data should be used. In the case of a magnetic tape where data was recorded, the data may not be completely erased. In addition, to detect the pilot signal, a position detecting signal is required. Thus, a pilot signal detecting circuit, a mis-detection preventing circuit, and the like are required.